The teratogenic drugs diphenylhydantoin (DPH) and acetazolamide produce deficiencies of bones in the limbs of mouse embryos from sensitive strains. The proposed studies are directed at identifying the mechanisms by which these drugs administered on the first day a limb is visible (day 9 of gestation) interrupt normal limb development. We know from previous work that the deformity produced by acetazolamide is first visible in the day 11 embryo and predict that DPH induced ectrodactyly of the limb will be visible at the same age. This means the drugs effect events in early limb development and not late events such as precartilage mesenchyme cell aggregation. We will look for possible effects of these drugs in early limb bud, including cell death in the notocord and somote, decreased migration of cells from somite to limb and altered patterns of blood vessel development. Day 10 somites and limb will be exposed to each drug in vitro and cultured for six days to determine whether either teratogen inhibits chondrogenesis in vitro and whether the effect of DPH correlates with the level of DPH or folate and the effect of acetazolamide can be blocked by a potassium-sparing diuretic. The pattern of distribution of 3H-DPH and 3H-acetazolamide will be determined to see if it correlates with the phenotypic effect of each drug in vitro and in vivo. Comparing the effect of DPH and acetazolamide in vitro and in vivo allows us to assess indirectly the role of an intact circulation and/or the migration of mesenchyme cells from somite into limb as mechanisms of the teratogenic effect of these teratogens. If a specific group of cells in the notochord, somite, limb or blood vessels appears to be a site of the early effect of either drug, these cells will be evaluated for an increased affinity for these drugs and for changes in cell shape.